Effect Of Steam On The Co-pyrolysis Of Coal And Biomass

Gas atmosphere was considered as the fluidized agent of various kinds of gas which were introduced into the reactor, which can be the inert gas, such as nitrogen, helium, etc. and can also be the reactive gas, such as water vapor, hydrogen gas and pyrolysis gas (CO, CO2, CH4, etc.). If gas atmosphere was added into the pyrolysis process of solid materials (biomass and coal), they could be involved in primary pyrolysis and second pyrolysis and then changed the pyrolysis process and product distribution. In this paper, the fast co-pyrolysis of white pine and sub-bituminous coal was performed in the free fall reactor. The study was focused on the effect of steam on co-pyrolysis product distribution and synergy between biomass and coal.The product distribution of co-pyrolysis of white pine and sub-bituminous coal was compared with and without steam at the pyrolysis temperature of600℃and biomass blending ratio (BR) of0.75. Compared with the experimental results from those without steam existence, the tar yield of co-pyrolysis with steam was increased. The water vapor atmosphere could promote the co-pyrolysis process. On the basis of this, the effect of different steam rate (2-5mL/h) on product distribution of co-pyrolysis was studied. With the increase of steam vapor rate, the tar and char yield increased firstly and then decreased, while the gas yield of co-pyrolysis decreased firstly and then increased. At the steam rate of3mL/h, the tar yield reached a highest value of22.1%, which was more6.9%than that without steam.At the steam rate of3mL/h, the co-pyrolysis experiments of white pine and sub-bituminous coal were studied at different temperature (500-700℃) and BR (0.25-0.75). In the range of500-600℃, the liquid yield increased and the char yield decreased with increasing of temperature. However, with further increasing of temperature, the reaction selectivity of steam was abated, which prejudiced the production of tar. The gas and liquid yield increased while the char yield decreased with the BR increasing at the steam rate of3ml/h and pyrolysis temperature of600℃. The pyrolytic liquid yield of BR of0.75was16.73%more than that of the BR of0.25. Therefore, the lower pyrolysis temperature and higher white pine mixed ratio were advantageous to the co-pyrolysis synergy of white pine and sub-bituminous coal and the generation of liquid tar.The char produced in the pyrolysis process had very high reactivity and also had certain catalytic role in the pyrolysis process. The co-pyrolysis experiments at the steam rate of 3mL/h were carried out under different char bed temperature with and without char bed. The results with steam showed that the gas and tar yield were increased while the water content in the liquid was decreased under char bed temperature of400℃. So the pyrolysis char had certain catalytic effect on the reactions of primary pyrolysis intermediate. This kind of catalytic effect could forbid the combination of H free radical with OH free radical into water and promote the combination of H free radical with other small molecules active free radicals into tar. However, when the char bed temperature was increased to500℃, the char promoted further secondary cracking of tar, which resulted in the increasing of gas yield and the decreasing of liquid yield.